/*

 * Copyright 1994-2006 Sun Microsystems, Inc.  All Rights Reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Sun designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Sun in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 */

package java.io;

/**

 * This abstract class is the superclass of all classes representing

 * an input stream of bytes.

 *

 * <p> Applications that need to define a subclass of <code>InputStream</code>

 * must always provide a method that returns the next byte of input.

 *

 * @author  Arthur van Hoff

 * @see     java.io.BufferedInputStream

 * @see     java.io.ByteArrayInputStream

 * @see     java.io.DataInputStream

 * @see     java.io.FilterInputStream

 * @see     java.io.InputStream#read()

 * @see     java.io.OutputStream

 * @see     java.io.PushbackInputStream

 * @since   JDK1.0

 */

public abstract class InputStream implements Closeable {

    // SKIP_BUFFER_SIZE is used to determine the size of skipBuffer

    private static final int SKIP_BUFFER_SIZE = 2048;

    // skipBuffer is initialized in skip(long), if needed.

    private static byte[] skipBuffer;

    /**

     * Reads the next byte of data from the input stream. The value byte is

     * returned as an <code>int</code> in the range <code>0</code> to

     * <code>255</code>. If no byte is available because the end of the stream

     * has been reached, the value <code>-1</code> is returned. This method

     * blocks until input data is available, the end of the stream is detected,

     * or an exception is thrown.

     *

     * <p> A subclass must provide an implementation of this method.

     *

     * @return     the next byte of data, or <code>-1</code> if the end of the

     *             stream is reached.

     * @exception  IOException  if an I/O error occurs.

     */

    public abstract int read() throws IOException;

    /**

     * Reads some number of bytes from the input stream and stores them into

     * the buffer array <code>b</code>. The number of bytes actually read is

     * returned as an integer.  This method blocks until input data is

     * available, end of file is detected, or an exception is thrown.

     *

     * <p> If the length of <code>b</code> is zero, then no bytes are read and

     * <code>0</code> is returned; otherwise, there is an attempt to read at

     * least one byte. If no byte is available because the stream is at the

     * end of the file, the value <code>-1</code> is returned; otherwise, at

     * least one byte is read and stored into <code>b</code>.

     *

     * <p> The first byte read is stored into element <code>b[0]</code>, the

     * next one into <code>b[1]</code>, and so on. The number of bytes read is,

     * at most, equal to the length of <code>b</code>. Let <i>k</i> be the

     * number of bytes actually read; these bytes will be stored in elements

     * <code>b[0]</code> through <code>b[</code><i>k</i><code>-1]</code>,

     * leaving elements <code>b[</code><i>k</i><code>]</code> through

     * <code>b[b.length-1]</code> unaffected.

     *

     * <p> The <code>read(b)</code> method for class <code>InputStream</code>

     * has the same effect as: <pre><code> read(b, 0, b.length) </code></pre>

     *

     * @param      b   the buffer into which the data is read.

     * @return     the total number of bytes read into the buffer, or

     *             the stream has been reached.

     * @exception  IOException  If the first byte cannot be read for any reason

     * other than the end of the file, if the input stream has been closed, or

     * if some other I/O error occurs.

     * @exception  NullPointerException  if <code>b</code> is <code>null</code>.

     * @see        java.io.InputStream#read(byte[], int, int)

     */

    public int read(byte b[]) throws IOException {

        return read(b, 0, b.length);

    }

    /**

     * Reads up to <code>len</code> bytes of data from the input stream into

     * an array of bytes.  An attempt is made to read as many as

     * <code>len</code> bytes, but a smaller number may be read.

     * The number of bytes actually read is returned as an integer.

     *

     * <p> This method blocks until input data is available, end of file is

     * detected, or an exception is thrown.

     *

     * <p> If <code>len</code> is zero, then no bytes are read and

     * <code>0</code> is returned; otherwise, there is an attempt to read at

     * least one byte. If no byte is available because the stream is at end of

     * file, the value <code>-1</code> is returned; otherwise, at least one

     * byte is read and stored into <code>b</code>.

     *

     * <p> The first byte read is stored into element <code>b[off]</code>, the

     * next one into <code>b[off+1]</code>, and so on. The number of bytes read

     * is, at most, equal to <code>len</code>. Let <i>k</i> be the number of

     * bytes actually read; these bytes will be stored in elements

     * <code>b[off]</code> through <code>b[off+</code><i>k</i><code>-1]</code>,

     * leaving elements <code>b[off+</code><i>k</i><code>]</code> through

     * <code>b[off+len-1]</code> unaffected.

     *

     * <p> In every case, elements <code>b[0]</code> through

     * <code>b[off]</code> and elements <code>b[off+len]</code> through

     * <code>b[b.length-1]</code> are unaffected.

     *

     * <p> The <code>read(b,</code> <code>off,</code> <code>len)</code> method

     * for class <code>InputStream</code> simply calls the method

     * <code>read()</code> repeatedly. If the first such call results in an

     * <code>IOException</code>, that exception is returned from the call to

     * the <code>read(b,</code> <code>off,</code> <code>len)</code> method.  If

     * any subsequent call to <code>read()</code> results in a

     * <code>IOException</code>, the exception is caught and treated as if it

     * were end of file; the bytes read up to that point are stored into

     * <code>b</code> and the number of bytes read before the exception

     * occurred is returned. The default implementation of this method blocks

     * until the requested amount of input data <code>len</code> has been read,

     * end of file is detected, or an exception is thrown. Subclasses are encouraged

     * to provide a more efficient implementation of this method.

     *

     * @param      b     the buffer into which the data is read.

     * @param      off   the start offset in array <code>b</code>

     *                   at which the data is written.

     * @param      len   the maximum number of bytes to read.

     * @return     the total number of bytes read into the buffer, or

     *             <code>-1</code> if there is no more data because the end of

     *             the stream has been reached.

     * @exception  IOException If the first byte cannot be read for any reason

     * other than end of file, or if the input stream has been closed, or if

     * some other I/O error occurs.

     * @exception  NullPointerException If <code>b</code> is <code>null</code>.

     * @exception  IndexOutOfBoundsException If <code>off</code> is negative,

     * <code>len</code> is negative, or <code>len</code> is greater than

     * <code>b.length - off</code>

     * @see        java.io.InputStream#read()

     */

    public int read(byte b[], int off, int len) throws IOException {

        if (b == null) {

            throw new NullPointerException();

        } else if (off < 0 || len < 0 || len > b.length - off) {

            throw new IndexOutOfBoundsException();

        } else if (len == 0) {

            return 0;

        }

        int c = read();

        if (c == -1) {

            return -1;

        }

        b[off] = (byte)c;

        int i = 1;

        try {

            for (; i < len ; i++) {

                c = read();

                if (c == -1) {

                    break;

                }

                b[off + i] = (byte)c;

            }

        } catch (IOException ee) {

        }

        return i;

    }

    /**

     * Skips over and discards <code>n</code> bytes of data from this input

     * stream. The <code>skip</code> method may, for a variety of reasons, end

     * up skipping over some smaller number of bytes, possibly <code>0</code>.

     * This may result from any of a number of conditions; reaching end of file

     * before <code>n</code> bytes have been skipped is only one possibility.

     * The actual number of bytes skipped is returned.  If <code>n</code> is

     * negative, no bytes are skipped.

     *

     * <p> The <code>skip</code> method of this class creates a

     * byte array and then repeatedly reads into it until <code>n</code> bytes

     * have been read or the end of the stream has been reached. Subclasses are

     * encouraged to provide a more efficient implementation of this method.

     * For instance, the implementation may depend on the ability to seek.

     *

     * @param      n   the number of bytes to be skipped.

     * @return     the actual number of bytes skipped.

     * @exception  IOException  if the stream does not support seek,

     *                          or if some other I/O error occurs.

     */

    public long skip(long n) throws IOException {

        long remaining = n;

        int nr;

        if (skipBuffer == null)

            skipBuffer = new byte[SKIP_BUFFER_SIZE];

        byte[] localSkipBuffer = skipBuffer;

        if (n <= 0) {

            return 0;

        }

        while (remaining > 0) {

            nr = read(localSkipBuffer, 0,

                      (int) Math.min(SKIP_BUFFER_SIZE, remaining));

            if (nr < 0) {

                break;

            }

            remaining -= nr;

        }

        return n - remaining;

    }

    /**

     * Returns an estimate of the number of bytes that can be read (or

     * skipped over) from this input stream without blocking by the next

     * invocation of a method for this input stream. The next invocation

     * might be the same thread or another thread.  A single read or skip of this

     * many bytes will not block, but may read or skip fewer bytes.

     *

     * <p> Note that while some implementations of {@code InputStream} will return

     * the total number of bytes in the stream, many will not.  It is

     * never correct to use the return value of this method to allocate

     * a buffer intended to hold all data in this stream.

     *

     * <p> A subclass' implementation of this method may choose to throw an

     * {@link IOException} if this input stream has been closed by

     * invoking the {@link #close()} method.

     *

     * <p> The {@code available} method for class {@code InputStream} always

     * returns {@code 0}.

     *

     * <p> This method should be overridden by subclasses.

     *

     * @return     an estimate of the number of bytes that can be read (or skipped

     *             over) from this input stream without blocking or {@code 0} when

     *             it reaches the end of the input stream.

     * @exception  IOException if an I/O error occurs.

     */

    public int available() throws IOException {

        return 0;

    }

    /**

     * Closes this input stream and releases any system resources associated

     * with the stream.

     *

     * <p> The <code>close</code> method of <code>InputStream</code> does

     * nothing.

     *

     * @exception  IOException  if an I/O error occurs.

     */

    public void close() throws IOException {}

    /**

     * Marks the current position in this input stream. A subsequent call to

     * the <code>reset</code> method repositions this stream at the last marked

     * position so that subsequent reads re-read the same bytes.

     *

     * <p> The <code>readlimit</code> arguments tells this input stream to

     * allow that many bytes to be read before the mark position gets

     * invalidated.

     *

     * <p> The general contract of <code>mark</code> is that, if the method

     * <code>markSupported</code> returns <code>true</code>, the stream somehow

     * remembers all the bytes read after the call to <code>mark</code> and

     * stands ready to supply those same bytes again if and whenever the method

     * <code>reset</code> is called.  However, the stream is not required to

     * remember any data at all if more than <code>readlimit</code> bytes are

     * read from the stream before <code>reset</code> is called.

     *

     * <p> Marking a closed stream should not have any effect on the stream.

     *

     * <p> The <code>mark</code> method of <code>InputStream</code> does

     * nothing.

     *

     * @param   readlimit   the maximum limit of bytes that can be read before

     *                      the mark position becomes invalid.

     * @see     java.io.InputStream#reset()

     */

    public synchronized void mark(int readlimit) {}

    /**

     * Repositions this stream to the position at the time the

     * <code>mark</code> method was last called on this input stream.

     *

     * <p> The general contract of <code>reset</code> is:

     *

     * <p><ul>

     *

     * <li> If the method <code>markSupported</code> returns

     * <code>true</code>, then:

     *

     *     <ul><li> If the method <code>mark</code> has not been called since

     *     the stream was created, or the number of bytes read from the stream

     *     since <code>mark</code> was last called is larger than the argument

     *     to <code>mark</code> at that last call, then an

     *     <code>IOException</code> might be thrown.

     *

     *     <li> If such an <code>IOException</code> is not thrown, then the

     *     stream is reset to a state such that all the bytes read since the

     *     most recent call to <code>mark</code> (or since the start of the

     *     file, if <code>mark</code> has not been called) will be resupplied

     *     to subsequent callers of the <code>read</code> method, followed by

     *     any bytes that otherwise would have been the next input data as of

     *     the time of the call to <code>reset</code>. </ul>

     *

     * <li> If the method <code>markSupported</code> returns

     * <code>false</code>, then:

     *

     *     <ul><li> The call to <code>reset</code> may throw an

     *     <code>IOException</code>.

     *

     *     <li> If an <code>IOException</code> is not thrown, then the stream

     *     is reset to a fixed state that depends on the particular type of the

     *     input stream and how it was created. The bytes that will be supplied

     *     to subsequent callers of the <code>read</code> method depend on the

     *     particular type of the input stream. </ul></ul>

     *

     * <p>The method <code>reset</code> for class <code>InputStream</code>

     * does nothing except throw an <code>IOException</code>.

     *

     * @exception  IOException  if this stream has not been marked or if the

     *               mark has been invalidated.

     * @see     java.io.InputStream#mark(int)

     * @see     java.io.IOException

     */

    public synchronized void reset() throws IOException {

        throw new IOException("mark/reset not supported");

    }

    /**

     * Tests if this input stream supports the <code>mark</code> and

     * <code>reset</code> methods. Whether or not <code>mark</code> and

     * <code>reset</code> are supported is an invariant property of a

     * particular input stream instance. The <code>markSupported</code> method

     * of <code>InputStream</code> returns <code>false</code>.

     *

     * @return  <code>true</code> if this stream instance supports the mark

     *          and reset methods; <code>false</code> otherwise.

     * @see     java.io.InputStream#mark(int)

     * @see     java.io.InputStream#reset()

     */

    public boolean markSupported() {

        return false;

    }

}